Liquid crystal display devices are being used in watches, calculators, various measurement instruments, automobile panels, word processors, electronic notepads, printers, computers, televisions, clocks, advertising board, etc. Typical examples of the liquid crystal display mode include twisted nematic (TN) mode, super twisted nematic (STN) mode, and vertical alignment and in-plane-switching (IPS) modes that use thin film transistors (TFTs). Recent years have seen a trend towards narrowing the cell gap (d) of liquid crystal cells to increase the driving speed of these liquid crystal display devices. Here, there is a limitation that the value (retardation) of the product (d×Δn) of the cell gap and the refractive index anisotropy (Δn) needs to be optimized. Thus, narrowing the cell gap (decreasing d) inevitably leads to increasing the value Δn. As such, there is need to increase the value Δn of the liquid crystal composition, and liquid crystal compositions having a larger Δn value than existing liquid crystal compounds are in demand.
Meanwhile, liquid crystal lenses that utilize birefringence of liquid crystal materials are available as one example of devices to which the liquid crystal compositions are applied. Liquid crystal lenses are being used as 2D-3D switching lenses, focusing lenses for cameras, etc.
These applications all involve sealing a liquid crystal composition between glass or film substrates and applying voltage to the liquid crystal composition aligned by an alignment film so as to cause alignment deformation of the liquid crystal composition and changes in the refractive index of the liquid crystal material so that the lens function is exhibited.
Examples of the substrates that seal in the liquid crystal material include a pair of common flat substrates, and a pair of substrates, one of which is processed into a lens shape. When both of the pair of substrates are flat, the arrangement of the electrodes is adjusted so that, in spite of the flat substrates, incoming light passing through the substrates is refracted by a liquid crystal layer aligned into a lens shape under application of an electric field that causes the liquid crystal molecules sealed between the substrates to align into the lens shape (PTL 1).
When a liquid crystal lens is used in 3D applications, the optical refraction caused by the liquid crystal lens and the binocular disparity are utilized so that the images on the right and on the left can be recognized by the right and left eyes so that the images can be recognized as a three dimensional object.
When the lens is used as a focusing lens for cameras, the refractive index is changed by adjusting the magnitude of the voltage applied so as to adjust the focal point distance.
With this type of liquid crystal lenses, the desired lens effect is obtained by using a thin cell when the change in refractive index caused by the change in alignment of the liquid crystal composition used therein is large. Thus, the liquid crystal composition used therein is required to have a high birefringence (Δn) not achievable by existing liquid crystal compositions. However, first of all, it is difficult to adjust Δn to a desired value; furthermore, it is extremely difficult to develop a liquid crystal composition that has practicable values for other physical properties such as the liquid crystal phase temperature range and viscosity, in addition to the required value Δn.